In recent years, in order to attain stable food supply, expectation has been drawn to plant factories that grow plants such as leafy vegetables in indoor facilities by hydroponic culture without being influenced by the weather, and various techniques have been proposed in this regard.
For example, Patent Document 1 proposes a hydroponic system in which culture panels in which a large number of holes are bored and seedlings are retained in each hole are vertically arranged in multiple stages, and panels are moved by sliding from top to bottom so that only the lowermost panel can be removed, whereby panels in which plants are ready to be harvested are sequentially removed. In the hydroponic system of Patent Document 1, since plants can be grown in a completely controlled environment in an enclosed space isolated from the outside, there is no fear of invasion by pathogenic bacteria and pests, and hence, spraying pesticides is not necessary. As a result, there are advantages that safe and stable production without use of pesticides can be attained, etc.